The present invention relates to slurry used in flattening by chemical mechanical polishing (hereinafter referred to as xe2x80x98CMPxe2x80x99), which is a step in the manufacturing of semiconductor devices.
When manufacturing a semiconductor device, a multilayered structure in which a plurality of layers such as insulating films and metal films are laminated on a substrate is generally formed. When forming the multilayered structure, in general it is vital to carry out flattening by CMP to remove unevenness after laminating an interlayer insulating film, a metal film or the like on the substrate, before proceeding with building up wiring on top of the flattened surface. In recent years, as miniaturization of semiconductor devices has advanced, it has become necessary for each layer on the substrate to have a flatness of ever increasing precision. Much is thus expected of CMP, and the number of CMP flattening steps used in a semiconductor device manufacturing process has increased.
In recent years, cerium oxide slurries containing cerium oxide particles as abrasives have come to be used as the slurries used in these CMP steps. Cerium oxide slurries are characterized in that the hardness of the abrasives is high and hence the surface being polished is easily scratched, but the slurry reacts with the SiO2 surface and hence the processing rate is high. Industrially, much is thus expected of cerium oxide slurries in terms of improving throughput. However, cerium oxide particles are heavy, having a density of 7.3 g/cm3, and hence there is a problem that when a slurry solution is prepared, the cerium oxide particles tend to settle, resulting in the solution separating into two layers. Use in an industrial plant is thus problematic, with, for example, the supply pipes for slurry solution tending to become clogged. Moreover, art in which the flatness of the polished surface is improved by adding a surfactant is currently being developed. However, if a surfactant is added, settling of the cerium oxide particles is accelerated, making usage impossible in a plant in which slurry is supplied to each of the CMP devices from one large slurry storage tank. Each of the CMP devices must thus have its own slurry supply system as ancillary equipment, using up extra space in the clean room.
An example of a publicly known cerium oxide slurry and using method thereof is given in Japanese Patent Application Laid-open No. H8-22970, which discloses a method in which protruding parts only of a film to be polished can be preferentially polished by adding an organic compound of molecular weight at least 100 having a COOH group, a COOM1 group (wherein M1 is an atom or functional group for which a hydrogen atom of a carboxyl group can be substituted to form a salt), an SO3H group or an SO3M2 group (wherein M2 is an atom or functional group for which a hydrogen atom of a sulfo group can be substituted to form a salt) to a slurry that has as the principal component thereof abrasives of CeO2 or the like. According to this method, as described in Reference Example 1 below, an insulating film layer formed on a patterned substrate can be polished extremely well, with dishing being suppressed. However, settling of the cerium oxide particles in the slurry occurs extremely quickly, with the slurry solution already having separated into two layers 10 minutes after preparation, that is, the slurry solution severely lacks stability.
Moreover, Japanese Patent Application Laid-open No. 2000-17195 discloses a cerium oxide slurry that contains cerium oxide particles, a copolymer of ammonium acrylate and methyl acrylate, and water. As described in Reference Example 2 below, this slurry has relatively good stability, not separating into two layers even when left for up to 3 days or more after preparation. However, when an insulating film layer formed on a patterned substrate was polished as above using this slurry, dishing was occurred heavily and a flat surface could not be obtained.
Moreover, Japanese Patent No. 3130279 discloses a slurry composition for polishing characterized by containing abrasives of ceria or the like and a polymer electrolyte having a charge of different ionicity to the charge associated with the abrasives, wherein the molecular weight of the polymer electrolyte is between about 500 and about 10,000, and the amount of the polymer electrolyte relative to the abrasives is between about 5 wt % and about 50 wt %. According to this slurry composition, as described in Reference Example 3 below, an insulating film layer formed on an unpatterned substrate can be polished at a good polishing rate. However, when an insulating film layer formed on a patterned substrate was polished as above using this slurry composition, dishing was occurred heavily and a flat surface could not be obtained. Moreover, regarding the state of dispersion of the abrasives, it was found that the composition starts to separate into two layers after leaving for about 1 hour after preparation.
As described above, there is still no cerium oxide slurry having cerium oxide particles as abrasives that is both capable of flattening an uneven film on a substrate with good precision and for which the dispersibility of the abrasives is good. As miniaturization of semiconductor devices advances, the wavelength of the light used in exposure becomes shorter and hence the depth of focus decreases, and thus if flattening is not carried out well, the width of the wiring will fluctuate either side of the specification value, adversely affecting the semiconductor device yield. Moreover, if the cerium oxide slurry has poor stability, then the slurry must be prepared immediately before use, resulting in ancillary equipment for supplying the slurry becoming mandatory for each CMP device, and hence in much space being required in the clean room, as described above. Moreover, this will also result in the drawback of a large amount of time being required for maintenance of the slurry supply equipment.
To resolve the above problems relating to the slurry supply equipment, the idea of installing the slurry storage tank outside the clean room and supplying slurry to each of the CMP devices from there has been investigated. In this case, because the storage tank is installed outside of the clean room in which the CMP devices are installed, it becomes necessary to supply the slurry from the storage tank to the CMP devices using supply piping of length tens of meters or more. If the abrasives in the slurry settle and build up in bends and dead parts of the piping, then the resulting deposit will eventually be forced through the piping and be used for polishing substrates, resulting in problems such as many scratches appearing on the substrate surface during polishing or the filter at the outlet of the supply device becoming clogged up. Moreover, the concentration of abrasives at the usage point will fluctuate, damaging the stability of the polishing. As a result of these things, to implement the above method successfully, it is extremely important for the slurry to have reasonably good storage stability. In particular, the slurry must not separate into two layers, solidify through flocculated settling, undergo a change in viscosity or the like, and flocculated settling must not occur in bends or dead parts of piping as described above even if the slurry is circulated through the piping for a prolonged period of time.
Due to the above, there have been hopes that a slurry that is capable of flattening an uneven film on a substrate with good precision, and that has good stability, not separating into two layers, solidifying through flocculated settling or undergoing changes in viscosity, could be provided.
The inventors of the present invention conducted studies into solving the above problems, and as a result made an unexpected discovery that led to the present invention, namely that when polyacrylates are used as surfactants in a slurry, if polyacrylates having different degrees of neutralization to one another are used and the total polyacrylate content is suitably adjusted, then a stable slurry can be obtained with no impairment of polishing characteristics.
Specifically, in a first mode of the present invention, a cerium oxide slurry comprising cerium oxide particles, a first polyacrylate in which more than 90% of the carboxyl groups in a polyacrylic acid have been neutralized with ammonia, a second polyacrylate in which 15% to 50% of the carboxyl groups in a polyacrylic acid have been neutralized with ammonia, and water, wherein the total content of the first polyacrylate and the second polyacrylate is 0.15 wt % to 1 wt % of the cerium oxide slurry is provided.
In the first mode of the present invention, the pH is preferably 4 to 6.
Moreover, in a second mode of the present invention, a cerium oxide slurry comprising cerium oxide particles, a first polyacrylate in which more than 90% of the carboxyl groups in a polyacrylic acid have been neutralized with ammonia, a second polyacrylate in which 15% to 50% of the carboxyl groups in a polyacrylic acid have been neutralized with ammonia, xanthan gum, and water, wherein the total content of the first polyacrylate and the second polyacrylate is 0.15 wt % to 5 wt % of the cerium oxide slurry is provided.
In the second mode of the present invention, the content of the xanthan gum is preferably 0.01 wt % to 1 wt % of the cerium oxide slurry.
Moreover, in the first and second modes of the present invention, the weight average molecular weight of the first polyacrylate is preferably 2000 to 10000, and the weight average molecular weight of the second polyacrylate is preferably 1000 to 3000.
Moreover, in the first and second modes of the present invention, the content of the first polyacrylate is preferably 0.01 wt % to 0.1 wt % of the cerium oxide slurry.
In a third mode of the present invention, a method of manufacturing an inorganic substrate, characterized by including a step of polishing the substrate using one of the above cerium oxide slurries, is provided.
In the third mode of the present invention, the substrate is preferably a semiconductor substrate having an SiO2 film.